Long-Lasting Orientation of Symmetric-Top Molecules Excited by Two-Color Femtosecond Pulses

Xu, Long; Tutunnikov, Ilia; Prior, Yehiam; Averbukh, Ilya Sh.

doi:10.3389/fphy.2021.689635

Cited by 8 publications

(11 citation statements)

References 75 publications

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“…The orientation factor at time t is obtained by averaging over all sample molecules (ensemble average). A more detailed description of the classical simulations can be found in [31,36].…”

Section: Three-dimensional Simulations a Numerical Methodsmentioning

confidence: 99%

“…Diverse optical methods have been developed to align and orient molecules in the gas phase under field-free conditions. A well-established route for orienting polar molecules is combining intense non-resonant laser fields with weak electrostatic fields [7][8][9][10][11][12][13][14][15][16]; another one involves using intense two-color laser pulses to induce molecular orientation via interaction with the molecular hyperpolarizability [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. For chiral molecules, it is possible to induce orientation by using laser pulses with twisted polarization [32][33][34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

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Echo-enhanced molecular orientation at high temperatures

Tutunnikov¹,

Xu²,

Prior³

et al. 2022

Preprint

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Ultrashort laser pulses are widely used for transient field-free molecular orientation -a phenomenon important in chemical reaction dynamics, ultrafast molecular imaging, high harmonics generation, and attosecond science. However, significant molecular orientation usually requires rotationally cold molecules, like in rarified molecular beams, because chaotic thermal motion is detrimental to the orientation process. Here we propose to use the mechanism of the echo phenomenon previously observed in hadron accelerators, free-electron lasers, and laser-excited molecules to overcome the destructive thermal effects and achieve efficient field-free molecular orientation at high temperatures. In our scheme, a linearly polarized short laser pulse transforms a broad thermal distribution in the molecular rotational phase space into many separated narrow filaments due to the nonlinear phase mixing during the post-pulse free evolution. Molecular subgroups belonging to individual filaments have much-reduced dispersion of angular velocities. They are rotationally cold, and a subsequent moderate terahertz (THz) pulse can easily orient them. The overall enhanced orientation of the molecular gas is achieved with some delay, in the course of the echo process combining the contributions of different filaments. Our results demonstrate that the echo-enhanced orientation is an order of magnitude higher than that of the THz pulse alone. The mechanism is robust -it applies to different types of molecules, and the degree of orientation is relatively insensitive to the temperature. The laser and THz pulses used in the scheme are readily available, allowing quick experimental demonstration and testing in various applications. Breaking the phase space to individual filaments to overcome hindering thermal conditions may find a wide range of applications beyond molecular orientation.

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“…The orientation factor at time t is obtained by averaging over all sample molecules (ensemble average). A more detailed description of the classical simulations can be found in [31,36].…”

Section: Three-dimensional Simulations a Numerical Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Echo-enhanced molecular orientation at high temperatures

Tutunnikov¹,

Xu²,

Prior³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

“…In practice, however, it will eventually be suppressed by additional physical effects, e.g., by intermolecular collisions in gas cell experiments. Related effects of long-lasting orientation have been recently investigated in chiral [10,[13][14][15] and other non-linear [10,16,17] molecules excited by non-ionizing THz and laser pulses.…”

mentioning

confidence: 99%

“…We quantify the degree of orientation of surviving neutral molecules using the thermally averaged quantum expectation value of cos(θ), cos(θ) . Further details on the quantum simulations can be found in [17,22] (also see Sec. I of the Supplemental Material [23]).…”

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confidence: 99%

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Ionization-induced Long-lasting Orientation of Symmetric-top Molecules

Xu¹,

Tutunnikov²,

Prior³

et al. 2022

Preprint

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We theoretically consider the phenomenon of field-free long-lasting orientation of symmetric-top molecules ionized by two-color laser pulses. The anisotropic ionization produces a significant longlasting orientation of the surviving neutral molecules. The degree of orientation increases with both the pulse intensity and, counterintuitively, with the rotational temperature. The orientation may be enhanced even further by using multiple delayed two-color pulses. The long-lasting orientation may be probed by even harmonic generation or by Coulomb-explosion-based methods. The effect may enable the study of relaxation processes in dense molecular gases, and may be useful for molecular guiding and trapping by inhomogeneous fields.

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Upper bound for permanent orientation of symmetric-top molecule induced by linearly polarized electric fields

Liang

Peng

2022

The Journal of Chemical Physics

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Many symmetric top molecules are among the most important polyatomic molecules. The orientation of a polyatomic molecule is a challenging task, which is at the heart of its quantum control and crucial for many subsequent applications in various fields.Most recent studies focus on the temporarily orientation achieved via the quantum revivals.In this work, we reveal the underlying mechanism behind the observed permanent orientation and discuss strategies for a higher degree of orientation.By a careful analysis of symmetry and unitary, it is possible to estimate an upper bound of $\braket{\braket{\cos\theta}}<{(2-\sqrt{2})}/{4}\approx 0.1464$ for a molecule in its thermal equilibrium states using a linear field. We show that this bound can be reached for an oblate symmetric-top molecule in the high temperature limit. To demonstrate different possible schemes, we take \ce{CHCl3} as an example. Simply with designed microwave fields, one can permanently orient \ce{CHCl3} with a degree of $\braket{\cos\theta}\approx 0.045$. We show that this value can be significantly increased by adding one or more pump pulses.

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Long-Lasting Orientation of Symmetric-Top Molecules Excited by Two-Color Femtosecond Pulses

Cited by 8 publications

References 75 publications

Echo-enhanced molecular orientation at high temperatures

Echo-enhanced molecular orientation at high temperatures

Ionization-induced Long-lasting Orientation of Symmetric-top Molecules

Upper bound for permanent orientation of symmetric-top molecule induced by linearly polarized electric fields

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